The present invention relates to a new process for the manufacture of fluoroalkyl (alk)acrylates.
Fluoroalkyl (alk)acrylates define compounds of formula: ##STR3## where R.sub.1 is a hydrogen atom, or an alkyl group having up to 4 carbon atoms, e.g., methyl, ethyl, propyl or butyl
n is between 1 and 20 and PA1 m is between 0 and n. PA1 m is between 0 and n, in the presence of at least one acid catalyst, at a temperature between 10.degree. C. and 30.degree. C. and during 3 to 120 minutes.
The most common of these compounds are fluoroalkyl methacrylate and acrylate. Where R.sub.1 is other than H, the compounds can be named as .alpha.-alkyl propenoic fluoroalkyl ester.
Several synthetic routes to these compounds are well known at present.
The first is an esterification reaction between an (alk)acrylic acid and a fluoroalcohol.
It is described particularly in the Japanese patent application 054,511 to 30.3.83, for the synthesis of 2,2,2-trifluoroethyl methacrylate, according to which methacrylic acid and 2,2,2-trifluoroethanol are reacted in the presence of a large excess of sulfuric acid. This reaction takes a very long time. The authors of this patent disclose 75 hours' reaction at 75.degree. C., for a yield which is only 73%.
A second synthetic route consists in reacting a (meth)acryloyl chloride with a fluoroalcohol. For example, U.S. Pat. No. 3,177,187 describes the process for preparing SYM-tetrafluorodichloroisopropyl acrylate and SYM-tetrafluorodichloroisopropyl methacrylate by reacting SYM-tetrafluorodichloroisopropyl alcohol with an acrylic or methacrylic chloride, optionally with an esterification catalyst which is preferably pyridine. The amount of catalyst may range from about 1.0 to 200%, preferably 5 to 50% by weight based on the amount of SYM-tetrafluorodichloroisopropyl alcohol charged. This preparation is effected at reflux temperature for a period of 5.5 hours to 10 hours. The yield of this reaction reaches only 67-75%. Moreover, the operating conditions for this reaction are complex. In fact, the hydrochloric acid produced during the reaction must be prevented from undergoing addition to the double bond, especially that of the (meth)acrylate. This is why the reaction must be carried out in the presence of an organic substance which reacts with hydrochloric acid, for example pyridine, to form a salt which must then be removed from the reaction mixture. Another disadvantage of this reaction lies in the ease with which acryloyl chlorides are hydrolyzed in the presence of moisture.